The instant invention relates to an apparatus and process for fixing toners or other materials on a medium. Subsequent to development of an image, the developed image is transferred to a receiving medium. After the transfer to the receiving medium, pressure and/or heat are applied to the receiving medium as the receiving medium and the developed image pass through a nip formed by a pair of rollers. By pressure and/or heat being applied, at the nip, to the receiving medium, the developed image is permanently fixed to the receiving medium.
As in any apparatus for fixing toners or other materials, the feeding and contact parameters, as the receiving medium passes through the nip, are critical. Without the proper feeding and contact parameters various problems, in and about the nip, result such as:
1. Defects in the fixed image caused by localized stresses in the nip mechanics during the fixing process. PA1 2. Inefficient thermal conductivity for internally heated rollers causing an increase in the time needed for the fixing roller to reach operational temperatures. PA1 3. Nip width directly related to the fixing pressure. PA1 4. Excessive drive torque that creates paper grab and deformation. PA1 5. Velocity changes in the nip causing image distortion. PA1 6. Static charge in the nip causing image distortion. PA1 7. Excessive roller wear. PA1 8. Artifacts such as rivers and lakes or toner smear caused by local stress in the nip. PA1 9. An arched nip resulting in paper curl or loss of paper stiffness. PA1 10. The need for large rollers to create wide flat nips. PA1 1. Minimal defects in the fixed image caused by localized stresses in the nip mechanics during the fixing process. PA1 2. Efficient thermal conductivity for internally heated rollers, thereby reducing the time needed for the heated roller to reach operational temperatures. PA1 3. A nip width minimally related to the fixing pressure. PA1 4. Reduced nip drive torque with minimal paper grab and deformation. PA1 5. Virtually no velocity change in the nip. PA1 6. Virtually no static charge in the nip. PA1 7. Virtually no roller wear. PA1 8. Virtually no artifacts such as rivers and lakes or toner smear. PA1 9. A symmetrical flat nip to prevent paper curl or lost of paper stiffness. PA1 10. A compact unit, using small rollers, capable of having a wide flat nip width.
In the past, to avoid feeding and contact problems, such as above stated, and to prevent the movement of the toner particles and the localized stress that caused defects or distortion of a image, one would change the compliancy of one or more of the rollers in the fixing assembly to lessen the effect of such process-related defects. Attempts made to increase the compliancy and to thereby lessen the fixing related image defects included making the elastomeric layers thicker and using an elastomeric foam material such as disclosed in U.S. Pat. No. 4,814,819. However, since fixing rollers are usually heated internally, it was difficult to obtain an elastomeric material that was sufficiently compliant while having a heat conductivity that efficiently provided the necessary heat to fix the toner images. Therefore, these attempted solutions proved unsatisfactory.